An image display system including a vehicle-mounted image capturing unit and a display unit on which an image captured by the image capturing unit is displayed is used as a device for assisting driving of a vehicle such as an automobile. Occasionally, a failure may occur in the image capturing unit, resulting in a state (hereinafter referred to as “freeze”) in which the captured image displayed on the display unit is fixed and does not change.
Image display systems exist that monitor changes in captured images obtained from the image capturing unit as the vehicle moves, in order to detect that a captured image has frozen. For example, the image display system described in Patent Document 1 includes a difference detection means that detects a difference between image frames that are successively output from an image capturing unit, and it is determined that a display image is frozen if no difference is detected between successive image frames while the vehicle is traveling.
When the vehicle is traveling, the number of frames of captured images used to determine whether or not a display image is frozen increases, thus increasing the overall data amount of captured images. To reduce the data amount for the freeze determination, in the image display system described in Patent Document 2, a white or black detection image that is inverted for each frame is added to a specific region of a captured image, and it is determined that freezing of a captured image has not occurred if a white image and a black image are repeatedly contained in successive captured images as detection images contained in the specific region.